Progress in achieving high-performance piezoresistive and capacitive flexible pressure sensors: A review

Electronic skin (e-skin) and flexible wearable devices are currently being developed with broad application prospects. Transforming electronic skin (e-skin) into true "skin" is the ultimate goal. Tactile sensing is a fundamental function of skin and the development of high-performance flexible pressure sensors is necessary to realize thus. Many reports on flexible pressure sensors have been published in recent years, including numerous studies on improving sensor performance, and in particular, sensitivity. In addition, a number of studies have investigated self-healing materials, multifunctional sensing, and so on. Here, we review recent developments in flexible pressure sensors. First, working principles of flexible pressure sensors, including piezoresistivity, capacitance, and piezoelectricity, are introduced, as well as working mechanisms such as triboelectricity. Then studies on improving the performance of piezoresistive and capacitive flexible pressure sensors are discussed, in addition to other important aspects of this intriguing research field. Finally, we summarize future challenges in developing novel flexible pressure sensors.